It is known to provide a seat belt tensioning device for tensioning an occupant belt restraint in the event of sudden vehicle deceleration. Many types of power sources have been proposed for forcibly tensioning the seat belt reel. In one form of tensioning device, the seat belt reel is forcibly rotated by a pyrotechnic device or squib to retract the seat belt, which tensions the seat belt about the occupant.
One such device is disclosed in co-pending application Ser. No. 09/024711, the disclosure of which is incorporated herein by reference. This device includes a piston connected by screw threads to the seat belt reel. Actuation of a pyrotechnic device moves the piston axially, which causes the threaded connection to rotate the seat belt reel to retract the seat belt. In this and other similar devices, the retraction energy characteristics are fixed.
It would be desirable to provide an improved pyrotechnic-operated seat belt tensioner which provides variable energy management (i.e. variable management of energy characteristics) to enable tailoring operation of the seat belt tensioner to different applications.